Background: Epigenetic alterations are common in prostate cancer, yet how these modifications contribute to carcinogenesis is poorly understood. We investigated whether specific histone modifications are prognostic for prostate cancer relapse, and whether the expression of epigenetic genes is altered in prostate tumorigenesis. Methods: Global levels of histone H3 lysine-18 acetylation (H3K18Ac) and histone H3 lysine-4 dimethylation (H3K4diMe) were assessed immunohistochemically in a prostate cancer cohort of 279 cases. Epigenetic gene expression was investigated in silico by analysis of microarray data from 23 primary prostate cancers (8 with biochemical recurrence and 15 without) and 7 metastatic lesions. Results: H3K18Ac and H3K4diMe are independent predictors of relapse-free survival, with high global levels associated with a 1.71-fold (P < 0.0001) and 1.80-fold (P = 0.006) increased risk of tumor recurrence, respectively. High levels of both histone modifications were associated with a 3-fold increased risk of relapse (P < 0.0001). Epigenetic gene expression profiling identified a candidate gene signature (DNMT3A, MBD4, MLL2, MLL3, NSD1, and SRCAP), which significantly discriminated nonmalignant from prostate tumor tissue (P = 0.0063) in an independent cohort. Conclusions: This study has established the importance of histone modifications in predicting prostate cancer relapse and has identified an epigenetic gene signature associated with prostate tumorigenesis. Impact: Our findings suggest that targeting the epigenetic enzymes specifically involved in a particular solid tumor may be a more effective approach. Moreover, testing for aberrant expression of epigenetic genes such as those identified in this study may be beneficial in predicting individual patient response to epigenetic therapies. Cancer Epidemiol Biomarkers Prev; 19(10); 2611–22. ©2010 AACR.

Docetaxel is the first-line chemotherapy for castration-resistant prostate cancer (CRPC). However, response rates are ∼50% and determined quite late in the treatment schedule, thus non-responders are subjected to unnecessary toxicity. The potential of circulating microRNAs as early biomarkers of docetaxel response in CRPC patients was investigated in this study. Global microRNA profiling was performed on docetaxel-resistant and sensitive cell lines to identify candidate circulating microRNA biomarkers. Custom Taqman Array MicroRNA cards were used to measure the levels of 46 candidate microRNAs in plasma/serum samples, collected before and after docetaxel treatment, from 97 CRPC patients. Fourteen microRNAs were associated with serum prostate-specific antigen (PSA) response or overall survival, according to Mann-Whitney U or log-rank tests. Non-responders to docetaxel and patients with shorter survival generally had high pre-docetaxel levels of miR-200 family members or decreased/unchanged post-docetaxel levels of miR-17 family members. Multivariate Cox regression with bootstrapping validation showed that pre-docetaxel miR-200b levels, post-docetaxel change in miR-20a levels, pre-docetaxel haemoglobin levels and visceral metastasis were independent predictors of overall survival when modelled together. Our study suggests that circulating microRNAs are potential early predictors of docetaxel chemotherapy outcome, and warrant further investigation in clinical trials.

Background: Methods: Results: Conclusions:

DNA methylation plays an important role in carcinogenesis and the reversibility of this epigenetic modification makes it a potential therapeutic target. To date, DNA methyltransferase inhibitors (DNMTi) have not demonstrated clinical efficacy in prostate cancer, with one of the major obstacles being the inability to monitor drug activity during the trial. Given the high frequency and specificity of GSTP1 DNA methylation in prostate cancer, we investigated whether GSTP1 is a useful marker of DNMTi treatment efficacy. LNCaP prostate cancer cells were treated with 5-aza-2′-deoxycytidine (5-aza-CdR) either with a single high dose (5–20 µM), every alternate day (0.1–10 µM) or daily (0.005–2.5 µM). A daily treatment regimen with 5-aza-CdR was optimal, with significant suppression of cell proliferation achieved with doses of 0.05 µM or greater (p<0.0001) and induction of cell death from 0.5 µM (p<0.0001). In contrast, treatment with a single high dose of 20 µM 5-aza-CdR inhibited cell proliferation but was not able to induce cell death. Demethylation of GSTP1 was observed with doses of 5-aza-CdR that induced significant suppression of cell proliferation (≥0.05 µM). Re-expression of the GSTP1 protein was observed only at doses of 5-aza-CdR (≥0.5 µM) associated with induction of cell death. Treatment of LNCaP cells with a more stable DNMTi, Zebularine required at least a 100-fold higher dose (≥50 µM) to inhibit proliferation and was less potent in inducing cell death, which corresponded to a lack of GSTP1 protein re-expression. We have shown that GSTP1 DNA methylation and protein expression status is correlated with DNMTi treatment response in prostate cancer cells. Since GSTP1 is methylated in nearly all prostate cancers, our results warrant its testing as a marker of epigenetic therapy response in future clinical trials. We conclude that the DNA methylation and protein expression status of GSTP1 are good indicators of DNMTi efficacy.